Final answer:
GH circulates freely in the blood as it is water-soluble while IGF-1 is bound to specific binding proteins. IGF-1 promotes amino acid uptake and protein synthesis, particularly in muscles and bones. Both hormones are tightly regulated by the hypothalamus.
Step-by-step explanation:
Human Growth Hormone (GH) and Insulin-like Growth Factor 1 (IGF-1) are crucial for regulating growth and development in the body. GH is a peptide hormone that circulates in the blood in a free form because it is water-soluble. Upon stimulation by GH, the liver produces IGF-1, which then plays a pivotal role in bone and muscle development. Unlike GH, IGF-1 is transported in the blood bound to specific binding proteins to extend its half-life and facilitate its delivery to target tissues where it promotes the uptake of amino acids and stimulates protein synthesis in skeletal muscle cells and cartilage.
While GH is directly responsible for speeding up the rate of protein synthesis in muscles and bones, IGF-1 activated by GH indirectly supports the formation of new proteins. The transport of IGF-1 is essential in mediating the actions of GH and promoting cellular proliferation, besides enhancing the differentiation of bone cells called osteocytes.
The regulation of GH levels is done by the hypothalamus through two hormones: growth hormone-releasing hormone (GHRH), which stimulates GH release, and growth hormone-inhibiting hormone (GHIH), also known as somatostatin, which inhibits GH release. These mechanisms are vitally important in maintaining the balance necessary for proper growth and development.